Add a note when people's timezones don't match up

[orta]

I got in a sup with someone from the UK (GMT) NYC (GMT + 5) and LA (GMT - 8) which is obviously bit tricky.

Maybe we can help let people know about a good time via by having sup pass a link like: https://www.timeanddate.com/worldclock/meetingtime.html?iso=20171106&p1=179&p2=136&p3=137